This invention relates to a side stream type condensing system in a power plant, and a method of operating the same.
In general, the hot well portion of a side stream type condenser in the side stream type condensing system of a steam turbine in the power plant is divided into the two independent wells of a first hot well and a second hot well. The first hot well stores therein condensed water which is the condensate of exhaust steam from the steam turbine. The condensed water is continuously fed from the first hot well to a water treatment equipment disposed in the exterior, and is treated here. This has been described in, for example, U.S. Pat. No. 4,055,043. It has also been known that the condensed water treated is fed to a heat exchange system which includes a gland steam condenser, a condenser air extractor, etc. The condensed water has its temperature raised by heat exchange here. The greater part of the condensed water is fed to the second hot well, and the remaining part is returned to the first hot well. The condensed water in the second hot well is fed to a main system in accordance with the operating state of the power plant.
As the features of the side stream type condenser wherein the condensed water purifying system is made independent of the main system as described above, there are mentioned that the condensed water purifying system can have the flow rate controlled independently of the water supply system of the main system, that since the pressure and the flow rate do not fluctuate abruptly, the performance of purifying the condensed water is enhanced, etc. Since, however, water levels need to be controlled in two places, how the water level controls during the normal operation and during the shutdown are made is a problem.
An an example of the water level controls of the hot wells of the side stream type condenser, the following method has been known.
The water level control of the first hot well is carried out in such a way that the flow rates of the condensed water from the condensed water purifying system to the first and second hot wells are regulated in accordance with the water level of the first hot well. The water level control of the second hot well is carried out in such a way that a condensed water storing tank which is connected to the main system and the first hot well is disposed, and that the quantity of return of the condensed water from the second hot well to the condensed water storing tank and the quantity of supplementary water from the condensed water storing tank to the first hot well are regulated in accordance with the water level.
In this water level control method, however, the water level control of the first hot well imparts fluctuations as disturbances to the flow rate of the condensed water flowing through the condensed water purifying system and the water level of the second hot well. In addition, notwithstanding the water level of the first hot well is directly relevant to the quantity of the supplementary water from the condensed water storing tank, the flow rate is controlled in accordance with the water level of the second hot well, so that the response of the water level control becomes slow. Moreover, the result of the water level control of the second hot well affects the water level control of the first hot well as a disturbance, which leads to the inconvenience that the two water level controls interfere with each other.
A further disadvantage is that when the side stream type condensing system is operated alone during the shutdown of the power plant, the water level controls of the hot wells become impossible.